HIV-1 (human immunodeficiency virus-1) infection remains a major medical problem, with an estimated 45 million people infected worldwide at the end of 2007. The number of cases of HIV and AIDS (acquired immunodeficiency syndrome) has risen rapidly. In 2005, approximately 5.0 million new infections were reported, and 3.1 million people died from AIDS. Currently available drugs for the treatment of HIV include nucleoside reverse transcriptase (RT) inhibitors zidovudine (or AZT or RETROVIR®), didanosine (or VIDEX®), stavudine (or ZERIT®), lamivudine (or 3TC or EPIVIR®), zalcitabine (or DDC or HIVID®), abacavir succinate (or ZIAGEN®), tenofovir disoproxil fumarate salt (or VIREAD®), emtricitabine (or FTC-EMTRIVA®); non-nucleoside reverse transcriptase inhibitors: nevirapine (or VIRAMUNE®), delavirdine (or RESCRIPTOR®), efavirenz (or SUSTIVA®), etravirine (INTELENCE®) and rilpivirine (EDURANT®), and peptidomimetic protease inhibitors or approved formulations: saquinavir, indinavir, ritonavir, nelfinavir, amprenavir, lopinavir, KALETRA® (lopinavir and Ritonavir), darunavir, atazanavir (REYATAZ®) and tipranavir (APTIVUS®), and integrase inhibitors such as raltegravir (ISENTRESS®), and entry inhibitors such as enfuvirtide (T-20) (FUZEON®) and maraviroc (SELZENTRY®). Several single pill combinations have been also approved, which include COMBIVIR® (contains lamivudine and zidovudine), TRIZIVIR® (contains abacavir, zidovudine, and lamivudine), Epzicom® (contains abacavir and lamivudine), TRUVADA® (contains tenofovir disoproxil fumarate and emtricitabine), ATRIPLA® (contains efavirenz, emtricitabine and tenofovir disoproxil fumarate) and COMPLERA® (contains emtricitabine, rilpivirine, and tenofovir disoproxil fumarate).
Each of these drugs can only transiently restrain viral replication if used alone. However, when used in combination, these drugs have a profound effect on viremia and disease progression. In fact, significant reductions in death rates among AIDS patients have been documented as a consequence of the widespread application of combination therapy. However, despite these impressive results, 30 to 50% of patients may ultimately fail combination drug therapies. Insufficient drug potency, non-compliance, restricted tissue penetration and drug-specific limitations within certain cell types (e.g., most nucleoside analogs cannot be phosphorylated in resting cells) may account for the incomplete suppression of sensitive viruses. Furthermore, the high replication rate and rapid turnover of HIV-1 combined with the frequent incorporation of mutations, leads to the appearance of drug-resistant variants and treatment failures when sub-optimal drug concentrations are present. Therefore, novel anti-HIV agents exhibiting distinct resistance patterns, and favorable pharmacokinetic as well as safety profiles are needed to provide more treatment options. Improved HIV fusion inhibitors and HIV entry coreceptor antagonists are two examples of new classes of anti-HIV agents further being studied by a number of investigators.
HIV attachment inhibitors are a novel subclass of antiviral compounds that bind to the HIV surface glycoprotein gp120, and interfere with the interaction between the surface protein gp120 and the host cell receptor CD4. Thus, they prevent HIV from attaching to the human CD4 T-cell, and block HIV replication in the first stage of the HIV life cycle. The properties of HIV attachment inhibitors have been improved in an effort to obtain compounds with maximized utility and efficacy as antiviral agents. A disclosure describing indoles of which the structure shown below for BMS-705 is representative, has been disclosed (Antiviral Indoleoxoacetyl piperazine Derivatives).

Two other compounds, referred to in the literature as BMS-806 and BMS-043 have been described in both the academic and patent art:
Some description of their properties in human clinical trials has been disclosed in the literature.
It should be noted that in all three of these structures, a piperazine amide (in these three structures a piperazine phenyl amide) is present and this group is directly attached to an oxoacetyl moiety. The oxoacetyl group is attached at the 3-position of 4-fluoro indole in BMS-705 and to the 3 position of substituted azaindoles in BMS-806 and BMS-043.
In an effort to obtain improved anti-HIV compounds, later publications described in part, modified substitution patterns on the indoles and azaindoles. Examples of such efforts include: (1) novel substituted indoleoxoacetic piperazine derivatives, (2) substituted piperazinyloxoacetylindole derivatives, and (3) substituted azaindoleoxoacetic piperazine derivatives.
Replacement of these groups with other heteroaromatics or substituted heteroaromatics or bicyclic hydrocarbons was also shown to be feasible. Examples include: (1) indole, azaindole and related heterocyclic amidopiperazine derivatives; (2) bicyclo[4.4.0] antiviral derivatives; and (3) diazaindole derivatives.
A select few replacements for the piperazine amide portion of the molecules have also been described in the art and among these examples are (1) some piperidine alkenes; (2) some pyrrolidine amides; (3) some N-aryl or heteroaryl piperazines; (4) some piperazinyl ureas; and (5) some carboline-containing compounds.
Method(s) for preparing prodrugs for this class of compounds are disclosed in Prodrugs of piperazine and Substituted Piperidine Antiviral Agents (Ueda et al., U.S. Publication No. 2005/0209246 or WO 2005/090367 A1).
A published PCT patent application WO 2003/103607 A1 (Jun. 11, 2003) discloses an assay useful for assaying some HIV inhibitors.
Several published patent applications describe combination studies with piperazine benzamide inhibitors, for example, U.S. Publication No. 2005/0215543 (WO 2005/102328 A1), U.S. Publication No. 2005/0215544 (WO 2005/102391 A1), and U.S. Publication No. 2005/0215545 (WO 2005/102392 A2).
A publication on new compounds in this class of attachment inhibitors (Wang, J. et al., Org. Biol. Chem., 3:1781-1786 (2005)) and a patent application on some more remotely related compounds have appeared WO 2005/016344 published on Feb. 24, 2005.
Published patent applications WO 2005/016344 and WO 2005/121094 also describe piperazine derivatives which are HIV inhibitors. Other references in the HIV attachment area include U.S. Publication Nos. 2007/0155702, 2007/0078141 and 2007/0287712, WO 2007/103456, as well as U.S. Pat. Nos. 7,348,337 and 7,354,924. A literature reference is J. Med. Chem., 50:6535 (2007).
What is therefore needed in the art are new HIV attachment inhibitor compounds, and compositions thereof, which are efficacious against HIV infection.
Of particular interest are new thioamide, amidoxime and amidrazone derivatives as HIV attachment inhibitor compounds, described herein. The compounds of the present invention are piperazine thioamide, amidoxime and amidrazone derivatives, which are believed to be structurally distinct from the piperazine aryl amide HIV attachment inhibitors set forth in the existing literature.